Water management influencing methane and nitrous oxide emissions from rice field in relation to soil redox and microbial community

Methane (CH4) and nitrous oxide (N2O) emissions from an irrigated rice field under continuous flooding and intermittent irrigation water management practices in northern China were measured in situ by the static chamber technique during May to October in 2000. The intermittent irrigation reduced total growing-season CH4 emission by 24.22% but increased N2O emission by 23.72%, when compared with the continuous flooding. Soil Eh and four related bacterial groups were also measured to clarify their effects on gaseous emissions. Three ranges of soil redox potential were related to gas emissions: below -100mV with vigorous CH4 emission, above +100 mV with significant N2O emission, and +100 to -100mV with little CH4 and N2O emissions. Intermittently draining the field increased soil oxidation, with a decrease in CH4 emission and an increase in N2O emission. In general the mid-season drainage slightly increased the populations of methanotrophs, nitrifiers, and denitrifiers but decreased that of methanogens.